Mandrake 9.2 ppp connection failure with USRobotics v.92 56k modem
 

I am having difficulty connecting to my ISP under Mandrake 9.2 (Burned copy from a friend who downloaded the ISOs). I've got a USR v.92 external modem tethered to my serial (com1/ttyS0) and am using pppd under KDE with Kppp to establish the connection. It dials up and begins handshake, but when it times out, I recieve the error that "connection timed out waiting for configuration request reply" or somesuch. I am able to make physical connection. If I use minicom to connect to the ISP, I get a prompt from their USR TotalControl rackmount modembank. Something is happening between the connection and the radius-auth request. I have 'worked-with' the ISP's 'support' people, and they tell me "we don't support linux, you're on your own."
Is there some known bug between the pppd under linux (esp Mandrake?) and newer proprietary radius authentication packages? If so, is there a known workaround? I am having quite a bit of trouble sussing this out.
Thanks

(Oh, by the way, I was able to connect under Mdk 7.1 about two years ago to this same ISP, but since then something has changed, and I am unable to connect under Mdk 7.1 either)